Overmodulation communication system



May 23, 1950 w. R. KOCH ovERuoDULATIoN COMMUNICATION SYSTEM 2 Shees-Sheet l Filed May 28, 1948 May 23, 1950 w. R. KocH 2,509,066

OVERMODULATION COMMUNICATION SYSTEM Filed May 28, 1948 2 Sheets-Sheet 2 "57 INVENTOR Patented May 23, 1950 UNITED STATES PATENT OFFICE OVERMODULATION COMMUNICATION SYSTEM Winnen a. Koch, Haaafmceld, N. J., assigner to Radio Corporation of America, a corporation of Delaware 13 Claims. l

invention relates to novel amplitude modulation signal receiving systems, particularly to such systems for receiving overmodulated signal-carrying waves.

One oi the objects of the invention is the provision of novel signal receiver systems for receiving and demodulating overmodulated waves without overmodulation distortion.

Still further objects of the invention are the provision of novel receiver systems for overmodulated waves having detector elements for detecting the lobes of the over-modulated waves, and interconnected for shifting the overmodulated waves and alternately forming upper and lower detected signal lobes in response to movement of the overmodulated lobes toward the zero amplitude level, after which the detected signal lobes are combined to reproduce the modulating signal.

The above as well as other objects oi the invention will best be understood from the following description of exemplifications thereof, reference being had to the accompanying drawings wherein:

Fig. 1 is an explanatory diagram illustrating some of the characteristics of over-modulated waves;

Fig. 2 is a block diagram schematically Ashowing a communication system embodying the invention;

Fig. 3 is a circuit diagram showing one form of signal receiver and demodulator exemplifying the invention;

Fig- 4 is a circuit diagram of a modification of a portion of the system of Fig. 3; and

Figs. 5, 6 and 7 are circuit diagrams similar to Fig. 3 of further modifications of a signal receiver and demodulator according to the invention.

When carrier waves are overmodulated in amplitude by intelligence conveying signal variations, the variations interfere with each other and cannot be faithfully reproduced in ordinary receiving systems. Overmodulating conditions develop for example in many cases when a radio wave is transmitted along the surface of the earth over a distance of the order of 100 miles. At such distances the waves in addition to moving directly along the earths surface are also transmitted by reflection from high altitude electromagnetically active atmospheric layers in such manner as to arrive at the receiver slightly later than the directly transmitted waves. The resulting phase difference between the two Waves causes some of the wave maxima or peaks to reach the receiver along one path just as wave minima reach it along the other, and cancellation or serious sup- 2 pression of these waves follow. When the phase difference is of the proper magnitude for causing suppression or cancellation of the carrier frequency waves with less suppression of the waves of adjacent frequencies, the signals received correspond to overmodulated waves.

Waves whose amplitudes are overmodulated by signals also may be deliberately produced by directly mixing the carrier waves with signal waves of larger amplitudes in such instances in which it may be desired to utilize overmodulated waves to produce a particular result. Under normal conditions the amount of energy carried by the modulated waves is distributed between the carrier waves and the signal waves in proportion to the relative amplitudes of these two waves before modulation. For exam-ple, when they are of the same amplitude, each contributes 50 percent of the resulting modulated Wave energy. In ordinary actual practice however equal amplitudes of carrier and modulating signal, or 100 percent modulation as it is generally called, does not operate satisfactorily and at present not more than about percent, or less, modulation is used. Furthermore, to allow for signal peaks when the loudest signals are produced, the modulation must be less than `percent to prevent distortion. By employing a receiver system embodying the invention however, overmodulated waves in which as much as two-thirds of the energy is contributed by the intelligence conveying modulations can be utilized for communication. Any such deliberately overmodulated waves accordingly carry higher intelligence-conveying signal energy than has hitherto been practicable. Furthermore, a large proportion of noise injected into an amplitude-modulated carrier wave communication system, results from external influences on the carrierwaves so that reduction of the carrier amplitude diminishes the noise level at the same time as it enables increase of the signal level.

This invention, however, relates only .to a system for receiving over-modulated waves, irre,- spective of the manner in which they may be produced. Accordingly, since the particular type of modulating system which may be employed to deliberately overmodulate a carrier wave, if so desired, forms no part of the present invention, the disclosure of a number of illustrative embodiments is restricted to a receiving system.

Fig. 1 is an illustrative explanation of some of the characteristics of over-modulated waves. At 20 is represented unmodulated carrier waves having displacements varying in uniform manner with respect to time, in accordance with the wave frequency. The amplitude of the unmodulated waves is represented by the dash line wave envelope 30, 3l, and is constant. At 22 the carrier waves are shown as modulated in amplitude by a modulating signal having a relative wave displacement indicated by the envelope waves 32, 33. Less than 1GO percent modulation is shown at 22 and it is seen that the carrier is here changed in amplitude, becoming alternately of larger and smaller amplitude than the unmodulated carrier 20. The minimum amplitude regions however, indicated at 34,' 35 are separated from each other so that at no point does the modulated wave amplitude reach the zero -displacement axis. At 1GO percent' modulation-the minimum displacement regions 34, 35, or 38, 39 would just touch the zero displacement axis without crossing it.

Overmodulated waves are represented at-24. The envelope 36, 31 correspondingr to the modulatingV signal shows still further variation in wave vjamplitucle; s o much so that the minimum vdisplacement regions or valleys 38 of the upper envelope 3B lare below the kZero displacement axis andthe minimum displacement regions or peaks "of the lower envelope 31 are above this axis.

An important consideration with respect to the degree of modulation is the manner in which it is demodulatedata receiver to reproduce the n- `telligence-conveying modulating signal. Almost all receivers` are at present equipped with rectifyingdemodulators or detectors, which function, 'foriexample by permitting passage of only one set of .the'lobes or envelope portions of the waves, such as '32, without permitting passage of the lobes 33 on the opposite side of the zero displace- `jmentaxis. The passed lobes are also filtered to removethe carrier 'wave high frequency ripple leaving a demodulated signal essentially duplicating the original modulating signal or envelope "132 Vorj33,`in the conventional case where the carrier'is about 80 percent modulated.

Withrovermodulated waves, however, the mere Arectification'asby blocking the'passage of the lower lobes, will not reproduce the original modulating signal. Instead, the resulting envelope waves such as 36 will have spurious lobe portions 39 which greatly distort them `and in many cases `renderthe demodulated signals unintelligible.

,Even with 100 Vpercent modulation, such 'de- ,tecting. action is undesirable because when the jlobeV amplitudesV become very small, Wave rectification'ceases tov follow the wave displacementas a proportional lor linear' function but introduces undesirable variations that also cause distortion.

'This is Va `principal reason for limiting conven- Waves, which may be provided by a signal source 40, are supplied to the input of a receiver as shown at 42. In the case Where the overmodulation is produced fortuitously, as in transmission for example, the source 4D maybe considered as the receiving antenna and associated circuits and apparatus. The receiver includes a modulatedcarrier-passing circuit generally in the form of Aan amplifier 44, the output of which includes detector elements for reproducing the -modulating signal and providing the demodulated output Vassembly V45 connected to provide a properly timed series of impulses 26. The shift arrange- `ment responds to these pulses and passes the modulated carrier waves alternately through the detectors 46,* 48 shifting the passage with each impulse. The impulses are timed so that shifting takes place at the instant the modulated carrier lobescross the zero displacementl level.

As so connected, the upperlobe detector 46 may be .arranged topass the'alternate. upper lobes 36 of the orermodulatedwaves while' the lower lobe detector 48 passes the alternate vlower lobes 3.8. Both sets of lobes are then combined in the demodulator output 50 toreconstitute the modulating signal waves, as shownat-52. yEii'icient reproduction isthereby provided according to the invention regardless of any'selective fading of the carrier or intentional or .inadvertent overmodulation of the carrier'duei toy othercauses. Communication with higher signal-to-noise iratics thanrhitherto possible'wit'h amplitudeimodulation systems, is also enabled.

An additional feature of the invention is the diminution in distortion fwith respect tov prior signal communication systems if/hiclfrjprovide percent or almost 10G percent lmodulation of carrierwaves. As pointed out above, `the deviation of the detector from the linear or proportional detecting Voperationgclose to the minimum amplitudecarrier levels injects distortion. 'With .waves 100 .percent modulated, these `distortions extend along a rela-tively long wave intervalcorresponding to modulatingsignal valleys or'min- Vma, where the signalV wavesare'reversing their motion and are changing direction at a relatively slow rate. According .to the 'invention thisnonlinearity of detection-takes place at a relatively steep portion of the modulating signal VWave where much less -of the wave is-subject to distortion. The time intervalbetween the Ventryof one lobe into the non-linear region and the emergence'of the next lobe from the non-.linear region is much smaller, than the non-.linear time interval of 10i) percent modulated waves. 1ecause of the shorter' time in-which-distortion ,is injected, the spurious signals thatv appearrare of higher frequency and a larger portion falls outside the frequency range of thesignalsreproduced-.and may be `filtered out so-as netto-interfere with the desired signals. Infact-in most amplitude modulated radio communication syStemS, the upper limit of signal frequencies reproduced is generallyquite low, about 560D tof6090cyclesper-second and any disturbances `at higher frequencies .are automatically excluded from the reproduced output.

Furthermore due to thepush-pull orrtandem action of the'double detection, the distortion introduced by non-linearityof the oppositelyuacting detection is in the form of two equal andopposite portions slightly displaced' in time. YAccordingly many of theharmonic"components of the Vdistortion arelneutralized :and do notl appear in the final-output.

l Fig."`3' shows "oneffform-V of--anlovermodulaton signal receiver circuit exemplifying the invention. According to this form of the invention, a modulated-carrier-passing circuit includes an input network 54, shown as the primary of a transformer 55 fed by the output or plate circuit of an electron discharge tube 56 according to conventional techniques and energized by means of a tube-operating D. C. plate voltage source B+. The transformer 55 has two secondaries, one, 59, connected to a detector shown in the form of an electron discharge diode including electron emitting cathode 62 and electron collecting anode 64 in space discharge tube 19. An additional secondary 90 of transformer 55 supplies in parallel the control electrodes 6I, 63 of a pair of electron discharge tubes 15, 11. Transformer output 58, shown as a resonant circuit, may be similar to the input circuit 54, and is connected to the diode elements 92, 64 through a load resistance 59, so that these diode-elements function to rectify cr detect the waves supplied and the detected signals appear across the resistance 59. Capacitance 91 may be connected across the resistance 59 to permit high frequency carrier ripples in the rectified waves to be by-passed and ltered out. The lobes of the rectied waves, in this case the negative lobes, are supplied to the input of an amplifier space-discharge section shown as included in the same tube 19, in the form of a second electron collecting plate 65 and a Control grid GS which controls the electron now from the cathode 62 to the second plate 65. The tube is energized by connecting its plate and cathode through a loading impedance 1| to a source of D. C. potential, indicated by the B-land ground connections.

At each time that the negative lobes of the carrier wave 25 of Figure 2 are about to cross the line representing the zero displacement level, the rate of change of the negative or lower envelope 31 is at a maximum so that there is produced a sharp current surging in the tube 10 and load impedance 1l. Voltage impulses corresponding to these current surges appear across load 1I and are transmitted through blocking condensers 12 and transformer secondary 69 to the control grids 9i, S3 of the tubes 15, 11. Blocking capacitor 12 isolates the high D. C. plate voltage of tube 19 from the low D. C. voltage of grids 6l, E3 and also establishes an A. C. ground return connection` from the low A C. potential side of secondary coil 69, in conjunction with a by-pass capacitor 19 across the plate circuit of tube 19.

Between the grids 6|, 63 a. D. C. blocking capacitor 14 enables these grids to operate at difv ferent bias potentials, as determined by their connections in a flip-flop network including bias resistances 19, 8l. The tubes 15, 11 are each shown as pentodes, having electron emissive cathodes, 82, 93, electron collecting plates 16, 19 and two electron flow controlling electrodes in addition to the control grids 9|, 63. Screen grids 84, 85 are shown as connected to suitable D. C. operating sources indicated by the -jsigns, and suppressor grids 86, 81 may be grounded or connected to the cathodes as in the figure. The cathodes 82, 33 of the tubes 15, 11 may be returned to ground through a biasing resistance 88, by-passed by capacitance 89 for minimizing any signal voltages that tend to appear across it. Tubes 15, 1l are operated by D. C. source 9|l having its positive terminal shown at B-l- -connected to their plates 16, 18, through the voltage dropping resistances 9 I, 92 and the signal loading networks' 93, 94 which in Fig. -3 are'shown as resonant circuits. The voltage dropping resistances 9|, 92 have their plate ends capacitively connected to ground through capacitances 95, 96 to complete the flip-flop networks.

The flip-nop or shifting action of the circuit is well-known and depends on the bias of the respective control grids 6l, 63 being supplied by the v voltage dropping resistances 8|, 19 in an output circuit of the opposite tube of this pair. In the form shown, the various circuit constants are so selected that when one of these tubes is conducting its plate circuit is so loaded that the plate side of the corresponding loading resistor 9|, 92 is lowered in Vpotential by an amount sufficient to keep the other tube from becoming conductive. The biasing resistance 88 causes each tubegrid to be biased negatively enough to substantially prevent the tubes from becoming conductive except when strong positive potentials appear at the voltage dropping resistances 19, 8l. Accordingly 'only one tube can become conductive at any one time. However, when a positive voltage pulse strong enough to overcome any cut-off bias is applied to the control grids 6 l 63, the tube previously non-conductive suddenly becomes conductive, causing its plate to fall in D. C. potential thereby transmitting a negative or falling pulse of larger magnitude to the control grid of the previously conducting tube and thereby cutting it 01T. The cutting off of the previously conducting tube causes its plate to rise in D. C. potential, delivering a positive pulse to the grid of the tube becoming conductive and sharpens the switching action. The delivery of a second control impulse from the input circuit to both control grids again shifts the switching action back to the original condition.

In the form shown in Fig. 3, the switching tubes 15, 11 not only alternate in conductivity but are connected to amplify the signal modulated carrier waves fed to the grids from the secondary winding 69 of transformer 55. Accordingly as the tubes alternately conduct, they also alternately deliver lobes of amplied signalmodulated carrier to their output networks 93, 94. These networks are respectively coupled to detectors 91, 98 where the lobes are rectified or demodulated, delivering the demodulated outputs to the respective detector loading impedances. Capacitances |02, |94, connected across these impedances lter out the high frequency carrier wave ripple, leaving only the modulating signal lobes. By proper interconnection of the detectors 91, 98 as shown, the alternate lobes indicated at 36, 38 in Fig. 2, are combined to reconstitute the desired signal. The load 99 is arranged to develop positive signal lobes at its cathode and with respect to its other side and the load |99 develops negative signal lobes at its plate end with respect to its cathode end which is grounded. The reconstituted output is taken between the cathode end of load 99 and ground.

Other forms of shifting detector apparatus may also be used. Thus the impulse generating elements may be modied to provide sharper impulses. For example control grid 66 may be biased so that only the extreme upper tips of the negative carrier wave envelope produced at the junction of adjacent ones of the lower lobes cause plate current surges to appear. The bias may be adjustable to provide the desired sharpness.

This is especially useful as for example where the incoming signal-modulated carrier waves yare subject to phase distortion or shifting in which I5 case the Wave amplitude may never. get down :annabee S7 .quite tot zero ,butblendsLsmoothly.:between-lobes -on the. same side fof the-zero 'amplitude axis. 'i-In 1 other words thewsmall sharplangles wh'ere adjacent lobes suchras-'SG' and 39 intersect. becomes -tude axis. For incoming' waves of.` suchcharacteristics, the impulseV generation canfbega'd-justed f to-ltake place at thenegative peaks between-jadjacent negative lobes, even though' l-thesejpeakS Sarenet at the zero amplitude level. r'The adjustable bias mayy be conveniently-supplied inr 'any well-knownmanner, as by a Variable" resistance inserted between the cathode 62 .and-the. resist- Vance 59. The variable biasing resistance maybe capacitively by-passed. 'Thebias `may alsobe ..1 supplied through. a -separateggridf resistance drectly to .the control: grid-66, in-which case -the i control gridlead from the detector load-59 should include a D. C.blocking capacitance to isolate the D. C. bias.

',As a further vmodification the switchingim- Y pulses and the modulated carrier lobes maybe fed in parallel'rather than in series. For example, the low A.A C. voltage side offsecondary winding Se may be coupled directly' to ground asa through a capacitance, and the plate 65 of tube 10 directly capacitivelycoupled to the grids 6|, 63. In this form, the capacitances 12, 13 are -not needed. Alternatively,r the coil El! x may be arranged to feed-the grids 61, 63 .in push-pulllor;

tandem, from the'coil ends.- the coil being-'connected to ground' at its center.

Fig. 4 shows one form of parallel feed arrangement for the switching impulses and carrier lobes.

The circuit is generally similar to -that of Fig. 3

above. and corresponding components -arefsimilarly numbered. Coil E0 is however, byepassed to ground at one end by means of capacitor -2--12 :and has its other end connected to the `switching and accordingly'held at a negative :bias-potentialwith respect to the cathode. The connection 'between-the grid 66? and `the detector-load fincludesV capacitor r2t$ which blocks `the posi- ".tive D. C. bias from the grid.

Other forms of switchingor flip-oparrangeiments may also lbe `usedas Adescribed for example inPucklesA ."IimeY bases, published in= 1943 vby rChaprn'an 1 and f Hall. Ltd.,` pp. 50 et seq. Thus :the switching-circuit rvneed not simultaneously A-be 'used asian.- ampliier but may-merely control separate'arnpliers orrdirectlyl effect detecting a'ctionp as :by biasing separate` amplifiers or-.the `detectors f93 `in-accordance ywith -the conduc- 'tive conditionfof thetubesl, 11. vFor` example,

' ea'chrdetector diode" 9.1,'Y .98: may be'iconnected-to l 'assume-the -.saine relative .potential as 'the ipotential between each of.. the; respectivercontrolgrids 61,2: @Briand the corresponding-cathode ofi tubes 51.5, ill. The. ipolarities:.may' rbe isoradjustedthat when fonemi-the. ftubes 15'; c1 1f is noni-conducting,

and amplifying circuit aswell. as-to-the impulse V:the associated'.` detector alsof cut-off, rand when f the tube :is conducting yits-gridY biasis. zero :and

Athe corresponding detector.. fedfdirectlyfrom the vinput at 55, operates lnormally. :fl-'capacitive :'coupling"between-theswitching tubes` and the detectors may be 'used toicontrollably` bias them only by means of' the switching; pulses, permitting both detectors to operate-when no shift Ycon- .trol..pulses;are received, asr for example, when lthe incoming r signals are not overmodulated.

Similandouble /detection 'may be provided by capacitively coupling. the impulse generator -of Fig.

`B-to the switching tubes. The shift control pulses which are inifthe formof approximately 'square waves, may be taken vfrom only-onefof-the switching ltubes andxmay be' supplied to both detectors r being switched.

The switching circuit connectionsto the switchingtubes 15, TI -may also bemodiiied `in .any well known manner, as by connectingthe switching load aresistances- 9|-, 92 and the voltage dropping resistancesls, 8l in the D. C. circuits supplying the screengrids 84, 85 instead of the plates 16, .18. inasmuch as-cutting oif the tube decreases thescreen currents as well asthe plate Lcurrents, similar' action is produced with either connection. The. suppressor-gridsmay likewise .form part'of the vswitching network-by taking crease in screen voltage,fincreasing the plate current-but causing fewer electrons to becollected vby Athe suppressor grid, making' the suppressor as well as the plate more negative. In this modification -the screen grids-may be connected as the inputs ofthe switching network and the suppressor'grids ifused-as the outputs are connected to ground through loading resistances =.--Fig.--5 exemplies a combined amplifying and switching circuit of` vthe-inventionin which the grid electrodes-of electron discharge tubes.

switching functionisA associated with the screen Pentode tubes l5, Tl, which may be the saineas those 4shownzin Fig. l, have theirplates '16, J3 connectedY to the` output detector circuits-including plate loading networks 93, Sii-directly from the common power supply 99, which maybe bypassed .by capacitor. S-Bl. Screen grids-@L85 are-.sup-

plied from the low signal potential sides ofthe respective. networks 93,` 94, through resistors 3-lil, 3-l l, and are-shown asloaded by ground return resistors 3--I 2', 3l 3=also -capacitivelyv bypassed. by lcapacitors 1t-Afl,.- 3-l5. UFeedback. frornfthe-screen load resistorsfto .the opposite grids is established by--the resistors 3-l6, .S-IL

`Thei-amplifyingmand switching arrangement is Y, otherwise similar to :that shown in Fig. 3.

The-embodiment illustrated in Fig. 5 alsoin- -cludes-a .push-pulleed tothe grids 45h63 of the vself-switching amplifier Vtubes .fl-5, 11. -Signal output coil Sii has its-ends connected to the respective grids 6i, through coupling ycondensers Si- 12, 3-l4,.andhas a'center tape-4! contype. The-eoiland its output are also shown as establishing -theB-b energizingcircuit of tube .Ii-'1li from a D. C. source B-Zs through isolatspenti-Ve ends-,oi -coil- Eil?. are completed by vgrou-nd connections asv shown.

The energizing. circuits The kswitching tubes 15,-- H5 may` .also be ofany -othersuitable..-.types,.such as. pentagrid electron discharge tubes in which the switching pulses and the signals to be amplified are independently supplied to separate control grids connected in separate switching and amplifying circuits. The tubes may also be of the tetrode or triode types if desired. Y

Fig. 6 is a circuit diagram of a further modication of the invention in which the switching circuit is distinct from the amplifying circuit, although both are controlled by the same electron discharge tubes. These tubes are shown at 4 15, A 'H as of the converter type having respective signal input grids li-Bl, 4 63 and switching grids d ll, 4 13 shielded from each other by screen grids 4 8G, 4 85 which also function as electron accelerating grids for the amplification action. Suppressor grids 4 ,86, 4 81 may also be provided and connected to the respective cathodes as in the examples of Figs. 3 and 5.

lThe switching grids 4 li 4 13 are connected in a flip-flop switching circuit with the reciprocal screen grids in a manner similar to that shown in Fig. 5 above. The tube-energizing B-lsource 9U may include series resistors 4 50, 4 5I bypassed by the respective capacitors 4 9l, A SZ. Signal supply for amplification is eiected by directly connecting one end of output coil Bil to both signal grids 4 61, 4 63 and returning the other end of the coil to the common cathodes of tubes eil-75, 4 11. In the form shown the signal return is through the bypass capacitor #3 62 while the coil return is conductively established to a tap on the cathode return resistor 4-38 to supply the desired D. C. bias to the signal grids with respect to the cathodes.

The switching grids 4 7! 4 13 are connected through capacitors 4 22, 4 24 for receiving the switching impulses appearing at the plate 65 of the impulse ampliiier tube lil. The impulse ampliiier circuit of tube 'I0 is shown as including an external bias source 4 30 for suitably controlling the amplification and improve the peaking action, as described above. The bias source 33 may be an adjustable bleeder on a D. C. supply and is shown as connected to the cathode 62 through an isolating resistor 4 26 for adjusting the positive potential of the cathode with respect to the grid. Aside from the independence of the amplication and switching circuits, the arrangement of Fig. 6 operates in essentially the same manner as that of Fig. 5.

Fig. 6 also includes a variation of the output detector network in accordance with the invention. The polarity of detection is arranged as by suitably connecting the detectors 91, 98 and their output loads- 99, |00 for causing the positive signal lobes to appear at one output load terminal, such as 4 90 with respect to the signal return, while the corresponding negative signal lobes appear at one terminal 4 94 of the other detector load. The two signal lobes are then combined by connecting the terminals 4 90,-

f--Bll in parallel to a common output connection 4 96 through a center-tapped impedance suchA as resistor 4 93.

The self-switching emplifying arrangement, as i Additional modifications include the use of the switching tubes such as i5, l1 to' amplify the detected outputs instead of the undetected modulated waves. This arrangement is suitable where these tubes are connected so as to apply separate bias voltages to detector 91, 98 and the detected signals accordingly appear at the control grids and can be derived from the plate circuits of these tubes.

Fig. 7 shows one modification of the invention in which the signal lobe switching is effected after detection. As shown the circuit includes an input supply in the form of band-pass transformer 5 55 which may supply input signals from a preceding amplier stage such as a conventional intermediate frequency amplier using electron discharge tube 56. The signals are supplied to and detected by the diode elements 5 53, s of electron discharge tube 5 51 and appear across the diode load 5 59 which is bypassed for high frequency carrier components by capacitor 5 5?. detector output may be taken as by means of an adjustable tap 5 6I and supplied for passage through another tube section which may be separate from or incorporated in the same tube envelope with the detector as shown. This additional section shown as a triode including cathode 5 60, control grid 5 66 and plate 5 65 iis operated as a phase splitter by inserting output loading resistors 5 1! 5 12 in the plate and cathode leads respectively and taking ofl output signals from points adjacent the tube ends of these loading resistors. The input may be capacitively supplied from the detector as by capacitor 5 49 and the grid return resistor 5 5I may be connected to an intermediate portion of the cathode output load so as to provide suitable bias voltage for the tube.

The split-phase output, so-called because the plate output signals are opposite in phase with respect to the cathode output signals, are separately applied to signal control grids 5 14, 5 15 of switching amplifier tubes 5 16, 5 11, shown as of the pentagrid type, each having an additional control grid 5 18, 5 19. The diiferent control grids of each tube are shielded from each other by screen grids 5 68, as in the similar arrangement of Fig. 6, and the signal grids which are supplied through blocking capacitors 5 8@ are returned to the tube cathodes which are connected together, through the separate grid return resistors 5 8l, 5 32. 'Ihe common cathodes may be returned to ground through the by-passed resistor 5 83..

Both switching ampiiers s u, 5 11 are en ergized in parallel from a D. C. source 90, the positive terminal of which is connected through a common plate loading resistor 5 84 to the tube plates. The final voutput from the load 5 84, which may be capacitively connected as shown, will contain alternately one signal lobe The switching generator of Fig. '7 is energized' from a signal lead such as one of the oppositely phased outputs of the phase splitter 5 51. The

Any selected fraction of the.

faisoegoccD switching i actuation.: may be supplied through blocking ,capacitor 5--85and pulse peakingdiodeL 5-86'biased. as'by the bleeder resistance chain` 5`8` to. pass 'only the sharp vertices between adjacent lobes of V:detected overmodulated waves.- Th'epeaked output across "loading resistor iin-83l maybe 'supplied to a trigger tube`5-89shown asV a triode which' interacts toalternatelycut'oi oneand then the other of a pair of triode li-ip-iiop tubes .5L-9B', 5-91.' Asshown; the three tubes iscut-of and. one isV conducting. Trigger tube 5-89's` supplied with 4sharp cut-off pulses thereby.. cutting 01T the flip-flop tube previously conducting. and generating a .sharp positive pulse. in its'` plate return resistor which pulse is transmittedlto the -grid;.of, theother. tube .rendering the othertube conductive just as the triggering.

impulseis completed... The action then repeats at the,neXt-triggering. impulse to. restore the original. condition, of the flip-nop, tubes -Ssl' 5-9i.

Theswitchingpulses generated bythe nip-flop tubes are .transmitted .to the switching amplifiers El-HL .5.-11 as. fby.. connecting the control grids 5-18, 5?.-19 ofth'ese amplifiers tothe controlV grids of the flip-nop. tubes and thesuccesslve lobes of the: detected Q.overmodulated;A waves are amplified, combinedand delivered.oppositelyphased to faithullyreconstitute the-,.overmodulating. sig.- nal.

The above-.described .features of the .invention maybecombined 'witheach other in different groupings; Thus for example, switching and 'ampli'cation in, the construction. of Fig.. 'T .may be Withthe self-switchingamplier `types as shown inligsef orA 5; or thepuls'e peaking. arrangement of Fig. I'l may be omitted if desired. AVC may be` incorporated inthealternately conductingistages... 5.-16,. 5.-.-1Tofji the construction. of

Figdl, as byiconnecting-a-.tap Yfrom resistor Eil-59; tot the junctionbetweem grid return resistors 5-8f|, 5--82` The.V AVC.. connection.` may be.

through an isolating resistonandthe grid returns may; be` .capactively by-passed to. ground to ,complete the.;input.circuitfor..the.A- Cl signals...

While severalexemplicationsiofetheinvention.

have .been -indicatedLand described above, itwill beapparent to those skilledfin the art .that other mor'iii'lcations.may'` be.. made. without departing fromthefscopecof theinvention as. setforth in thefappended..claims..y

What-is claimed is: Y

tude:and-having.upperand-lower trains-.of signal lobes; circuit'means having-.an-.input for-receiv-` ing and passing said overmodulated waves; de-

tector .elements for detectingthe lobes of atleastl one train of said.signalflo'bes;` and`l shift .means connected'with saidcircuit meansf'for response to movements of a lobe envelope toward the zero amplitude level for alternately shifting thepassage of said lobes through. .the receiver system andjoperatingsaid detector .elements in' alternation soith'at the lobes passed are alternately above and. below zero signalv level;` said system having an. output in which. the alternately( passed; lobes are .combined to reproduce the modulation signals.

2.1In an amplitude modulation signal receiver system for receiving and deriving Ymodulation signals.. from .overmodulated electric `Waves having.

upper andlower signal lobes; circuit. means having an input for..receivingsandpassing said overmodulated'. waves; detector.. elements. forming part of saidcircuit. means. and.. selectably connected for separately detecting the upper and the lower .signal lobes of said overmodulated lvvaves; andA shift means. connectedfrwith. said circuit meansand responsive to .movements Yof a lobe envelopeA towardthe.. zero.. amlplitudelevel for alternately shifting. .the passageof overmodulated waves-through .the detectorelements to= alternately. detectsaid .upper and'saidlovver lobes;- said detector elements having an output in which separatelydetected lobes are combined toreproduce the -modulationsignaLQ 3. `A11 amplitude modulation receiver as defined by. claim V2 in whichthefdetector. elements Yinclude two `separate. detector. circuitshaving independent input means. and a. combined output circuit; andfthe shift means. is connectedforalternately preventing signal passage'to. one andthen the otherof said .independent input means..

4.. Anamplitude modulation receiver as defined by. claim 3..in..vvhich the shift means includes a tvvo-channelflip-flop network connected for actuation by movements of signal lobesthrough the zero amplitude level to alternatelyopen one channeljand substantially simultaneously close the.

input circuit of .eachsectionbeingcoupled to the.

circuit-means for receiving the signal waves; and the sections being also coupled tothe impulse supply means .forcausing saidsections to simultaneously amplify and shift the` signal. waves through .the detector circuits.

6. A amplitude'modulation..receiver. as defined by claim.2.in which. .the ,shift .meanslincludes a flip-nop network connectedforresponse to shift impulses, and 'also includes impulse supply means having. detector structurecoupled .to the circuit means for passing-.only one set of vsignal lobes and developingpulsesas the signallobes approach the zero amplitude-level..

7L .An amplitudemodulation receiveras dened by claim .6 in .which the .detector structure is coupled to. passV the lower lobes; and the .impulse supply meansincludes space .dischargeamplication elements connected for amplifying the peaks of the lower lobes.

8. An amplitude modulation receiver as dened by claim 7 in which the space discharge amplification elements are biased for passing only those portions of the lower lobe peaks which are approximately at the zero amplitude level.

9. In an amplitude modulation signal receiver system for receiving and deriving modulation signals from overmodulated electromagnetic waves having corresponding signal-modulated envelopes respectively!l of positive and negative polarity relative to a common zero displacement axis, each of said envelopes normally being on one side only of said axis but as a result of said overmodulation a, relatively small portion of each of said envelopes being on an opposite side of said axis from a relatively large portion thereof, said receiver system comprising, a rst signal detector for demodulating waves having envelope portions on one side of said axis, a second signal detector for demodulating waves having envelope portions on the other side of said axis, switching means responsive to a diminishing relatively small amplitude of one of said envelopes to impress said waves alternately upon said detectors in proper polarity to eiect demodulation of substantially all of said Waves dened by both portions of one of said envelopes, and a, common output circuit for said detectors in which to develop the complete modulation signal.

10. An amplitude modulation receiver as dened in claim 9, in which respective load circuits are provided for said detectors, said detectors being connected to develop similarly polarized voltages in said respective load circuits, and said common output circuit comprises the oppositely polarized connection of said load circuits.

11. An amplitude modulation receiver as dened in claim 10, in Which said switching means comprises two electronic tubes coupled for alternate operation and having output circuits coupled respectively to said detectors.

12. An amplitude modulation receiver as defined in claim 11, in which said switching means includes an impulse generator responsive to said small envelope amplitudes and is coupled to the input circuits of said electronic tubes to operate said tubes in alternation.

13. An amplitude modulation receiver as dened in claim 12, in which said impulse generator develops a series of impulses similarly polarized to initiate space current conduction in a nonconducting one of said tubes, and the input and output circuits of said tubes are cross-connected so that the initiation of current conduction in one of said tubes renders a conducting tube non-conducting. g

WINFIELD R. KOCH.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,360,7401 Hartley Nov. 20, 1920 2,113,214 Luck Apr. 5, 1938 2,275,298 Hugenholtz Mar. 3, 1942 2,302,852 Goddard Nov. 24, 1942 

